Process of regenerating a liquid catalyst



United States Patent Oflice Patented Feb. 18, 1964- 3,121,673 Plt UQESL @F REGENERATHNG A LIQUID QATALYST Wilhelm Riernenschneider, Lothar Hiirnig, and Emmerich Palszth'ory, Frankfurt am Main, and Aliens Steinmetz, Kelliheim, Tauuus, Germany, assignors to Farbwerlie Hoechst Alrtieugesellschatt vorrnals Meister Lucius dz Brtining, Frankfurt am Main, Germany, a corporation oi Germany No Drawing. Filed Apr. 14, 1959, Ser. N 806,255 filaims priorit application Germany Apr. 23, 1958 7 Claims. (til. 204-157) The present invention relates to a process for oxidizing olefins to aldehydes, ketones and acids.

it has already been proposed to oxidize ethylene catalytically by means of an argentiferous catalyst to ethylene oxide, or by means of an oxidation catalyst other than a silver-containing catalyst at a raised temperature to obtain mixtures of formaldehyde, acetaldehyde, formic acid, acetic acid and other products. In these processes, however, acetaldehyde or acetic acid cannot be produced in a yield interesting from an economical point of view. Our experiments have revealed that the oxida tion carried out under such conditions in the presence of a noble metal catalyst likewise involves small yields of acetaldehyde, and the relative proportion of formaldehyde obtained generally preponderates.

it is also known that compounds of palladium, platinum, silver, or copper form complex compounds with ethylene. Furthermore, the formation of acetaldehyde was observed in decomposing a potassium-platinum-complex compound. Other unsaturated compounds may favor the complex formation. in this case stoichiometric reactions are concerned yielding the noble metal as such.

It has also been suggested to reduce palladous chloride by means of ethylene in the presence of water to palladium metal. In this reduction the formation of acet aldehyde was observed. It is also known that palladous chloride dissolved in water can be reduced rapidly and completely to palladium by means of propylene, even if propylene is admixed with nitrogen or air, or by means of isobutylene. It is indicated that carbon dioxide is not evolved in any one of the aforesaid reductions.

in a number of prior applications, various processes are described according to which carbonyl compounds can be obtained from the corresponding olefins, i.e. olefins having the same number of carbon atoms as the carbonyl compounds, in a good yield and, if desired, in a continuous manner by contacting said olefins with an oxidizing agent, a liquid catalyst having an acid to neutral reaction and comprising water, a compound of a noble metal belonging to group Vl'll of the periodic table such as a salt of platinum, iridium, rhodium, ruthenium, or preferably palladium, and a redox system. The redox system preferably comprises at least one salt of at least one metal which can form several stages of va-lences under the reaction conditions applied, wherein the metal is bound to an anion of a non-metallic element. In this connection reference is made to the following applications, all relating to a Process for oxidizing olefins to aldehydes, ketones and acids:

Serial No. 747,116, filed July 8, 1958; Serial No. 750,150, filed July 22, 1958; Serial No. 763,691, filed September 26, 1958, now abandoned; Serial No. 768,624, filed October 21, 1958; Serial No. 770,007, filed Gctober 28, 1958, now US. Patent No. 3,076,032; Serial No. 769,912, filed October 27, 1958; Serial No. 769,554, filed October 27, 1958, now abandoned; Serial No. 738,488, filed January 23, 1959, and Serial No. 803,096, filed March 31, 1959.

Reference is furthermore made to a process accord ing to which ethylene is contacted at an elevated temperature in a neutral to acid medium with molecular oxygen in the presence of Water and an inorganic redox system comprising at least one compound of a metal which can form several stages of valences under the reaction conditions applied and which is at least monovalent in its reduced stage of valence. Such process is, e.g., described in application Serial No. 765,272, filed October 6, 1958.

in the aforesaid applications the term carbonyl compounds is used in its broad sense, i.e. it covers not only aldehydes and ltetones, but also carboxylic acids such as acetic acid.

Sometimes it can be observed that the activity of the catalyst subsides after some time in view of by-products being formed in the course of time, which have a relatively high boiling point and accordingly are enriched in the catalyst liquid. This may imply disturbances in operation of either physical nature, for example obstruction of conduits or nozzles, or of chemical nature, such as the formation of oxalic acid, which gives rise to the precipitation of heavy metal compounds, for example copper oxalate, and thereby inactivates part of of the contact-active substance. in addition thereto, other yroducts may form which reduce the yield.

We have now found that such didiculties may be avoided when the oxidation is carried out in the presence of a liquid and the catalysts may readily be reactivated if the lay-products formed are oxidatively removed by the action or" nitrogen-oxygen compounds, halogens and any combination thereof, eg. nitric acid or nitrous gases, chlorine or nitrogen-oxygen halides, such as NO'Cl or mixtures of these oxidizing agents.

Furthermore, it is possible to produce the oxidation agent, for example nitrosyl chloride, only during the reaction. The goal of this mode of execution is not the oxidation of the reduced stages of the redox system added, although this oxidation takes place simultaneously, but rather a far reaching destruction of scarcely to nonvolatile by-products, if possible to acetic acid or carbon dioxide.

The reaction may be accelerated by the simultaneous action of a radiation source rich in enengy, for example, ultraviolet light, which is especially important if the reaction is carried out at a relatively low temperature, for example at between C. and C. It is preferred to use a mercury-quartz lamp as source of irradiation during the action of the oxidizing medium.

This mode of execution may be modified by operating in the presence of oxygen or air, for example by injecting these gases into nitric acid or by using a mixture of chlorine and/ or a nitrous gas with oxygen or air.

The lay-products formed can be destroyed in a simple manner by heating the catalyst, or possibly precipitated or separated parts thereof, with the oxidizing agent, which is used in an amount depending on the quantity of products to be oxidized and is preferably within 2% to 50% of the amount of the catalyst. in order to obtain a sulficient reaction velocity it is suitable to use a working temperature within the range of 90 C. and 250 C.; a temperature higher or lower than indicated above may also be used, but in the latter case it is advantageous to Work under pressure. After the oxidation has been terminated, it may be advantageous but is not necessary to remove the nitrogen-oxygen compound or the chlorine. This may be done by injecting an inert gas or oxygen or air. Alternatively, the catalyst solution may be evaporated to dryness and read usted to the initial amount by the addition of water or a hydrous solvent or of catalytic and/or activating substances, such as halogenated acetic acids or quinones, which may be substituted by sulfonic and/or carboxylic acid groups, or of salts of any one of the aforementioned substances.

The oxidation with nitric acid or a nitrous gas easily gives rise, especially in case of a deficiency of chlorine ions, to the formation of relatively insoluble metal oxide salts, for example copper oxychloride. Accordingly, it may be useful, after removal of the nitrogen-oxygen compounds, to add hydrochloric acid so as to readjust to the initial or any desired concentration of halogen ions, for example chlorine ions. Such readjustment is especially recommended in the case where the finished catalyst has been freed from nitric acid and nitrous gases by evaporation. If chlorine or mixtures of chlorine and nitrogen-oxygen compounds have been used as oxidizing agent, the aforesaid variant can be so modified that a subsequent readjustment to the desired concentration of chlorine ions can be dispensed with.

The present method of regeneration is important for those processes in which the oxidation is carried out in the presence of aqueous liquid, i.e. either at a liquid contact medium, in which the catalytically active substances are dissolved in water or water-containing solvents or at those which contain absorption media, such as active carbon or kieselguhr, or which contain solid substances in a hydrous solvent, but preferably in water (slime cataly t), so that the catalytically active substances are present in a high concentration. Furthermore it may be applied not'only to one-stage processes but also to two-stage processes or to any other modification described in any one of the aforementioned applications, such as the method of carrying out the process in one or more streaming tubes. For example, the non-converted gases may be circulated, such as a gas which is free from oxygen or which contains a few percent of unreacted oxygen.

In the aforesaid process as compounds of the noble metals of group VIII of the periodic table there may be mentioned, for example, salts of palladium, iridium, ruthenium, rhodium, or platinum, i.e. of metals the stable valence of which is at most 4. Salts of these metals are believed to be capable of forming addition compounds or complex compounds with olefins, such as ethylene. The reaction may likewise be carried out in the presence of a noble metal from which, in the course of the reaction, the reactive compounds are formed. The redox system may comprise one or more compounds of one or more metals which may appear in various oxidation stages under the reaction conditions, for example salts of copper, iron, cerium, antimony, manganese, molybdenum, chromium, titanium, tin, thallium, cobalt, nickel, uranium, mercury, vanadium, lead, osmium, or selenium. Inorganic redox systems other than the latter, preferably in admixture with compounds of other of the metals specified above, such as sulfite/sulfate, or arsenite/arsensate systems and/or organic redox systems, for example azobenzene/hydrazobenzene, or quinones or hydroquinones of the benzene, anthraceneor phenanthrene series may also be used.

For example it is possible smoothly to use a catalyst in which the ratio of the sum of redox metals, especially the sum of copper and iron, to the noble metal, especially palladium, is at least 15:1, preferably 25-500z1. It is, however, preferred to use a catalyst containing copper salts, in which the ratio of copper to palladium is above :1, for example above :1 and preferably 50:1 to 500:1, or-even above these ranges. This method of operating is more economic in view of the fact that the expensive palladium salt need only be used in a minor amount. 7

While ethylene yields acetaldehyde, propylene yields preponderantly acetone and propionaldehyde. aand ,B-butylene yield preponderantly methylethylketone, the a-butylene yielding also butyraldehyde. Isobutyraldehyde canbe obtained from isobutylene. Furthermore higher olefins, such as pentene and its homologs, cyclohexene or styrene, or mixtures of gases, containing olefins, or diolefins, may be reacted in the same manner as the aforementioned olefins. Preferably olefins are used which contain at least one hydrogen atom at the carbon atoms, which are part of the olefinic bonds.

'In the afore-said process the olefins may, for example, be oxidized by oxygen, if desired in the form of air, which is the cheapest oxidizing agent, or in the form of air enriched with oxygen. The use of air is, however, confined to certain limits, if the unreacted gases are circulated, inasmuch as nitrogen concentrates as ballast material.

The reactants may be diluted by one or more gases inert towards the reaction, for example by nitrogen, carbon dioxide, methane, ethane, propane, butane, isobutane, cyclohexane, benzene, toluene, etc., or by carbon monoxide and/or hydrogen. If such gas mixture contains carbon monoxide, oxygen should be present at least in an amount as is necessary to convert carbon monoxide to carbon dioxide and the desired amount of the olefin to aldehyde. In this reaction the carbon monoxide is partially converted to carbon dioxide. If hydrogen is present, the major amount of hydrogen remains unaltered, whereas a small portion thereof reacts with formation of water and another small portion with hydrogenation of the olefins.

To prevent explosions, it is preferred to work outside the range of eXplos-ivity, for example with a content of oxygen of 820%, or 844% under pressure, and to circulate unreacted gas which consists substantially of nonconverted olefin, if desired in admixture with other inert gases.

The oxidation of the olefins may be supported or carried out by addition of an active oxidizer, which is broadly listed in the above mentioned applications. For example, ozone, peroxy compounds, such as hydrogen peroxide, etc., are mentioned. By the addition of such compounds the reformation of the higher oxidation stage of the noble metal or of the metals contained in the redox system, such as copper and/or iron, is facilitated.

Furthermore a dispersing agent, such as an alkylphenyl sulfonate and/or a protective colloid and/or a finely dispersed solid substance like active carbon and/ or kieselguhr, may be added to the catalyst, in the olefin oxidation, whereby the aggregation of larger particles is counter-acted.

The anions present are preferably anions of nonmetallic elements. For example, the catalyst may contain chlorine ions or halogen ions other than chlorine, such as bromine ions, nitrates or chlorateor perchlorate radicals or mixtures of these anions, for example, with sulfate or acetate radicals. Sometimes it is especially advantageous to use a catalyst which contains perchlorate was.

It is often advantageous to add, prior to or during the oxidation of the olefins, a compound yielding anions under the reaction conditions applied, for example an inorganic acid, preferably a mineral acid, such as sulfuric acid, nitric acid or a volatile acid such as hydrochloric acid or hydrobromic acid, or a salt such as ammonium chloride, am-

monium bromide, zinc chloride, aluminum chloride, iron chloride, chromic chloride, titanium tetrachloride, sodium hydrosulfate, a halogen such as chlorine, bromine, or bromo-trichloride, or a halogen-oxygen compound, for example hypochlorous acid, bromic acid, chlorine dioxide or thionyl or sulfuryl chloride, or also an organic substance, preferably a saturated aliphatic halogen compound of low molecular weight, such as ethyl chloride, propyl chloride, butyl chloride, acetyl chloride, benzoyl chloride, propionyl chloride or phosgene. Such addition enables a possible decrease of anions to be counteracted and the lifetime of the catalyst to be prolonged.

Instead of or preferably in addition to the supply of compounds yielding anions it is possible to influence the reaction to a certain extent by modifying the ratio of olefin to oxygen. The moment at which the olefin to oxygen ratio is modified, can be readily determined by continuously measuring the pH, which may be performed by any known method.

If the pH-value decreases, it is easily possible to readjust tie optimum pl-l-range by adding either more :iygen or less olefin, or by combining these two steps. If the pH increases, the optimum pH-range can be readjusted inversely.

The aforesaid process is carried out at reduced pressure or, more preferably, at atmospheric or raised pressure, at elevated temperature, with special advantage at temperatures Within the range from 50 to 160 C., preferably between 50 and 120 C., in an acid to neutral medium, preferably at a pH-value Within the range between 0.8 and 5. if desired, conditions outside the ranges indicated above may be applied, for example at temperatures of l70 to 180 C. or 40 C.

In the olefin oxidation sometimes the presence of a salt, such as alkali metal or alkaline earth metal halides, e.g., LiCl, NaCl, KCl, CaCl MgCl or other salts such as ZnCI or of haloge ated acetic acids, preferably trichloroaeetic acid and/ or bromoacetic acid, or salts thereof, may prove advantageous. The halogenated acetic acids or the salts thereof have a very strong dissolving action on C-uCl and their use involves a smooth reaction and an increased conversion.

in order to increase the olefin concentration in the reaction space, higher concentrations of metal salts binding oiefins, such as ethylene, e.g., copper-, iron-, mercuryor iridium-compounds, especially halides, or the sulfates, the latter especially when mercury is concerned, or organic solvents which are preferably miscible with water, for example acetic acid, methylethylketone, or other ketones, monoor polyhydric alcohols, acylic others or dirnethyl formamide, may be present in the catalyst medium.

if catalysts are used in the olefin oxidation, which do not contain compounds of the noble metals of group VIII of the periodic table as described in the above-mentioned patent applications, it is generally advisable to operate at higher temperatures than in the presence of such compounds. Generally, in this case, the reaction temperature is between 80 and 253 (3., preferably between 130 and 200 C. Pressures up to 200 atmospheres (gauge) or even more. may be anolied The present process may be carried out from time to time or continuously, for example by discharging a pant, advisably a small part of the catalyst, reactivating it according to the invention and then recirculating it into the system. The lifetime of the catalyst may, however, be prolonged and the reactivation accordingly be carried out less often it it is irradiated by rays rich in energy, e.g. by ultraviolet light. Such radiation which may also cornprise Xrays, activates especially the oxygen, increases its oxidizing activity, and promotes both the reaction with the olefin and a possible oxidative destruction of byproducts, for example oxalic acid.

The apparatus used in the process of invention snould be made of a material which is not corroded by the catalyst and the reactants and preferably has a sufii cient thermal conductivity. Since the catalysts used mostly contain noble metal compounds, for example palladium compounds, it is less suitable to use \the usual metals and alloys as construction material, since there is the risk that these less noble metals, in the presence of water and at the indicated temperatures, precipitate the noble metal salt used in the catalyst, and that they themselves are converted into salt form.

In order to avoid corrosion in the apparatus used, it is often suitable to use glass vessels or enamelled vessels. The reaction may also be carried out in brick-lined vessole or, under suitable reaction conditions, in vessels the insides of which are lined with plastic material, for example,

one, hardenable phenol, cresolor Xylenol-formaldehyde resins or other acidproof resins. As brick-lining there may be used, for example, ceramic material, carbon bricks impregnated with hardenable artificial resins and similar known materials.

The following examples illustrate the invention but they are not intended to limit it thereto.

Example 1 (A) A catalyst containing, per liter of water, 2 grams of P Cl 120 grams of CuCI QI-E O, 30 grams of Cu(CH CO0) .2l-l O and 20 grams of F6013 is used over a period of 1000 hours to produce acetaldehyde at C. under atmosphenic pressure from ethylene and oxygen which are applied in a molar ratio of 4:1, the yields obtained at the end of this period are about 20%.

(B) 1 liter of the catalyst described sub (A) and used over a period of 1000 hours is heated on the steam bath for 2 hours with 209 cc. of 60% nitric acid and then evaporated to dryness While passing through air. The dry substance is made up to 1 liter by adding Water, and the required amount of hydrochloric acid is added so that the chlorine ions appear in a concentration corresponding to that of the starting catalyst. The catalyst so regenerated yields, after a short induction period and under the conditions set forth sub (A), about 35% of acetaldehyde.

Example 2 The procedure is the same as described sub Example 1(3) with the exception that a mercury quartz lamp immeme-d into the bath is used to irradiate the catalyst while oxidizing it with nitric acid. Under the conditions described sub Example 1(A) about 35-40% of the ethylene are converted to acctaldehydc.

Example 3 1 liter of a catalyst used over a period of 1000 hours as described in Example 1(A) is introduced into a titanium autoclave and heated for 1 hour at l50-l60 C. under elevated pressure with cc. of 60% nitric acid, so that the nitric acid is still present in the liquid phase. The liquid is removed from the autoclave, evaporated to dryness as set forth in Example 1(A), water is then added, and subsequently hydrochloric acid to adjust the solution to the initial concentration of chlorine ions. The catalyst so regenerated is used under the same conditions as described in Example 1(A) and gives yields of about 40%.

Example 4 The procedure i the same as described sub Example 1(3) with the exception that instead of the nitric acid grams of nitrosyl chloride are vaporized and then introduced into the catalyst. The catalyst is then evaporated to dryness and further treated as set forth in Example IMB). Under the conditions described sub Example 1(A) about 33% of the ethylene are converted to acotaidehyde.

W e claim:

1. A process of regenerating a liquid catalyst for conversion of an oletinic carbon atom of an iolelinic hydrocarbon to a carbonyl group by contacting said hydrocarbon in a neutral to acid medium with oxygen and said catalyst, said liquid catalyst consisting essentially of (a) a salt of a noble metal of the group consisting of palladium, iridium, ruthenium, rhodium and platinum and (b) as a redox system, an inorganic salt of a metal showing several valence states under the reaction conditions applied, said catalyst being dissolved in water at least in part, said process consisting essentially of contacting the catalyst with an oxidizing agent of the group consisting of nitric acid, nitrosyl chloride and mixtures thereof.

2. Process as defined in claim 1 wherein the catalyst is contacted with the oxidizing agent at a temper atu re in the range from 90 C. to 250 C.

3. Process as defined in claim 1 wherein the catalyst is contacted with nitnic acid.

4. Process as defined in claim 1 wherein the catalyst is contacted with nitrosyl chloride.

5. Process as defined in claim 1 wherein the treated catalyst is subsequently evaporated to dryness.

6. A process as defined in claim 1 wherein the catalyst is contacted with the oxidizing agent in the presence of ultraviolet radiation.

7. A process as :in claim 1 wherein said catalyst contains chlorine ions, and wherein losses of chlorine ions occurring during regeneration are compensated by adding hydnogen chloride to the catalyst.

0 .3 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Phillips: Amer. Chem. 101117., vol. 16, pp. 255-77 (1894) (pages '265-72 relied upon).

Chntt: Chem. Abstracts, vol. 48, p. 5067 (1954). 

1. A PROCESS OF REGENERATING A LIQUID CATALYST FOR CONVERSION OF AN OLEFINIC CARBON ATOM OF AN OLEFINIC HYDROCARBON TO A CARBONYL GROUP BY CONTACTING SAID HYDROCARBON IN A NEUTRAL TO ACID MEDIUM WITH OXYGEN AND SIAD CATALYST, SAID LIQUID CATALYST CONSISTING ESSENTIALLY OF (A) A SALT OF A NOBLE METAL OF THE GROUP CONSISTING OF PALLADIUM, IRIDIUM, RUTHENIUM, RHODIUM AND PLATINUM AND (B) AS A REDOX SYSTEM, AN INORGANIC SALT OF A METAL SHOWING SEVERAL VALENCE STATES UNDER THE REACTION CONDITIONS APPLIED, SAID CATALYST BEING DISSOLVED IN WATER AT LEAST IN PART, SAID PROCESS CONSISTING ESSENTIALLY OF CONTACTING THE CATALYST WITH AN OXIDIZING AGENT OF THE GROUP CONSISTING OF NITRIC ACID, NITROSYL CHLORIDE AND MIXTURES THEREOF. 